Embodiments of the subject matter disclosed herein relate to turbo-machines, methods for fixing bundles of a turbo-machines, and covers for the openings of barrel casings.
A centrifugal compressor or pump comprise an external pressure barrel casing that accommodates a diaphragm bundle. Typically, the barrel casing defines a cylindrical cavity and the diaphragm bundle has a cylindrical shape. The diaphragm bundle typically comprises at least rotor and stator with their impellers, seals and fluid channels.
The cylindrical cavity, defined by the barrel casing, has an open at one side, typically the circular lateral side. This open allow the insertion of the bundle. The open is closed after insertion of the bundle by mean of a cover, which typically has the form of an end wall structure.
The barrel casing contains stationary and rotatable components. Stationary components are in general rigidly fastened to the barrel casing; whilst rotatable components are generally held up by bearings positioned in the cover.
The barrel casing of a turbo-machine in operation tends to expand radially, due to the rise of temperature and pressure at its inside; whilst the cover tends to shift axially. This can bring to a misalignment of stationary components with respect to rotatable components, affecting the working conditions of the machine. In fact, it is essential that the center axis of the cover is kept at all times in alignment with the central axis of the barrel casing.
FIG. 1 shows a solution known from the prior art, where barrel casing 10 is firmly fixed to the cover 20 (after insertion of the bundle 5) by mean of shear ring 30. The shear ring 30 is a ring composed by two, or four (or even more) symmetrical portion, that when joined together in contiguous way form the whole ring. The inner surface of the barrel casing 10 (namely on the surface facing the volume containing the bundle 5) is provided with a circumferential groove 70 adapted to receive the portions composing the shear ring 30. The outer surface 20a of the cover 20 is provided with a similar circumferential groove 40, which is adapted to receive partially the shear ring, when the turbo-machine is assembled. The outer surface of the barrel casing 10 is provided with a plurality of screws 80 (typically one screw per portion composing the shear ring), to move (partially) the shear ring from the groove 70—on the barrel casing 10—to the groove 40—on the cover 20. It worth noting that the groove 40 on the cover 20 has a depth adapted to receive only part of the cross section of the shear ring 30.
Thus the steps for assembling a turbo-machine of this kind are: insert the various portion of the shear ring on the groove 70; insert the bundle 5; mount the casing 20 on the open side of the barrel casing 10; fix the barrel casing 10 to the cover 20 by mean of the shear ring 30, threading the screws emerging from the outer surface of the barrel casing 10. The shear ring 30 is thus partially engaged in the groove 40 and partially engaged in the groove 70, blocking, in this way, the axial movement of the bundle 5 and the cover 20.
In this configuration, the depth of the groove 70 has to be dimensioned to contain completely the cross section of the shear ring 3, in order to perform the insertion of the bundle 5 and the successive fixing. Furthermore, un-engaging screws must be provided (not shown in FIG. 1) to raise up the shear ring 30 on the groove 70 on the barrel casing 10, for dismounting the bundle 5 to perform the maintenance operations.
Thus, the wall of the barrel casing 10 must have a certain minimum thickness to realize the groove 70 of the proper dimension. This solution increases the overall dimension of the turbo machine, the amount of material required to produce the barrel casing 10 and impacts with dimensional constraints of the turbo-machine.
Therefore there is a need for a system for fixing a cover in a turbo machine barrel casing that is easier to mount and dismount, thus allowing saving on maintenance, and does not require an increase in size at the mouth of the barrel casing.